(i) Field of the Invention
The present invention relates to an organic electroluminescent component, specifically an organic electroluminescent component using a particular aromatic methylidene compound which has the ability of high brightness luminescence in low voltage application with excellent stability.
(ii) Description of the Related Art
An electroluminescent component which uses an electroluminescent phenomenon of substances is self-luminescence type unlike a liquid crystal component. Accordingly, its visibility is high and, therefore, it is possible to obtain clear indication when used for displays. Because it is a complete solid state component, it has the characteristics such as excellent impact resistance. In future, the electroluminescent component is expected to find use widely for a back light of thin type displays or liquid crystal displays or plane light sources.
One of electroluminescent components which are now put into practical use is a dispensing type electroluminescent component in which inorganic materials such as zinc sulfide are used. However, these dispersing type electroluminescent components need comparatively high a.c. voltage for their drive and, therefore, have problems such as complicates driving circuits or low brightness. Now, these are not widely put into practical use.
Meanwhile, organic electroluminescent components using organic materials have been spotlighted since C. W. Tang et al. proposed a component having a laminate structure in which an electron-transporting organic fluorescent substance and a positive hole-transporting organic substance are stacked and both carriers for electrons and for positive holes are injected into the fluorescent substance layer to generate luminescence in 1987 [C. W. Tang and S. V. VAN Slyke, Appl. Phys. Lett., Vol. 51, p. 913-915 (1987); Japanese Patent Application Laid-Open No. Sho-63-264629]. It is described that luminescence of at least 1000 cd/m.sup.2 may be obtained under a driving voltage of not more than 10 V in these components. Various investigations for these materials have been carried out actively since the aforementioned proposal. As a result, various materials and component structures are now proposed and researches for their practical use are performed actively.
On the other hand, in fact, organic electroluminescent components using the organic materials proposed still have various problems. Examples of these problems include the following phenomena. Functions of the components deteriorate to lower luminescence brightness in a driving state or even in a non-driving state, i.e. during storing. Alternatively, in a driving or non-driving state, there happens the deterioration that non-luminescent regions called dark spot appear and grow up, which, finally, lead to a short circuit in the components that causes ruptures. These phenomena are considered to be essential problems in the materials used there. In the present state, it is hardly recognized that the components have sufficient lives for their practical use. Therefore, their practical use is restricted to devices in which a comparatively short life may be accepted.
Alternatively, mention is made of another problem that, in the case where the components are colored, systems or materials therefor are not sufficiently prepared. In order to solve these problems and to attain their wide practical use, it is an important technical object to research for new high functional luminescent materials and electric charge transporting materials.